Diet may affect the risk of several chronic human diseases but additional research is needed. This project examines effects of diet on neurodevelopment, cancer risk, and in relation to risk of amyotrophic lateral sclerosis (ALS). Summary: Fish contains omega-3 fatty acids, which are essential for brain development. Because fish can also be a source of neurotoxins, such as methylmercury, most studies of neurodevelopment have considered fish intake only as a surrogate measure of neurotoxin exposure. Thus the potential beneficial effects of fish on long-term neurodevelopment have not been well characterized. We evaluated the association between maternal prenatal fish consumption and neurodevelopment among offspring in a cohort of 7421 British children born in 1991-1992. All children born to mothers resident in Bristol and the surrounding areas between April 1991 and December 1992 were eligible for the ALSPAC study. Expectant mothers were recruited during routine prenatal health visits and completed an enrollment questionnaire. An estimated 85% of the eligible population participated. The present investigation was restricted to singleton, term (>37 completed weeks gestation) children whose mothers completed prenatal questionnaires on diet and postnatal developmental assessments when the child was 15 and 18 months of age (n=10,092). Fish intake by the mother and child was measured by questionnaire. The child?s neurodevelopment was assessed using the MacArthur Communicative Development Inventory at 15 months of age and the Denver Developmental Screening Test at 18 months of age. Mercury was measured in umbilical cord tissue for 1054 children. Accomplishments: Total mercury concentrations were low and were not associated with neurodevelopment. Fish intake by the mother during pregnancy and the infant postnatally were independently associated with slightly higher mean developmental scores on many of the subtests assessed. These data suggest that when mercury exposure is low, moderate fish intake during pregnancy and infancy may benefit neurodevelopment.